Airbags for motor vehicles are known and have been used for a substantial period of time. A typical construction material for airbags has been a nylon fabric, coated with an elastomer such as polychloroprene or silicone. The fabric used in such bags is typically a woven fabric formed from synthetic yarn by weaving practices which are well known in the art.
The coated material has found acceptance because it acts as an impermeable barrier to the inflation medium. This inflation medium is generally a nitrogen gas, generated from a gas generator or inflator, which is conveyed into the cushion at a relatively warm temperature. The coating obstructs the permeation of the fabric by the hot gas, thereby permitting the cushion to rapidly inflate, without undue decompression, during a collision event.
Airbags may also be formed from uncoated fabric which has been woven in a manner that creates a product possessing low permeability, or from fabric that has undergone treatment, such as calendering, to reduce permeability. Fabrics which reduce air permeability by calendering or other mechanical treatments after weaving are disclosed in U.S. Pat. No. 4,921,735 issued May 1, 1990 to Bloch and U.S. Pat. Nos. 4,977,016 issued Dec. 11, 1990; 5,010,663 issued Apr. 30, 1991 and 5,073,418 issued Dec. 17, 1991 to Thornton et al. (all incorporated by reference).
The coating of a fabric with an elastomer such as polychloroprene or silicone typically requires the application of that elastomer from a solution in a volatile solvent. This solvent must then be evaporated and the elastomeric system cured. This process of evaporation and curing typically requires the application of heat over a considerable period of time. As will be appreciated, a lengthy curing process serves to significantly raise the cost of the coated fabric and complicates the overall production process which leads to inherent reductions in efficiency. While, as indicated above, it is possible to weave a fabric in a structure which is sufficiently tight to substantially reduce air permeability, it is generally accepted that weaving alone should be followed by a separate heating and cooling process to allow the yarns to shrink, thereby forcing them into a tighter construction. Such steps are detailed in U.S. Pat. No. 5,356,680 to Krummheuer et al. (incorporated by reference). The need for such an additional step is, of course, undesirable due to the length of time which it requires and the additional complexity which it introduces to the process.
Another problem which is encountered with traditional coated fabric wherein relatively high levels of polychloroprene or silicone are applied or a tightly woven fabric undergoes a substantial heat shrinking procedure, is a loss of flexibility in the fabric. As will be appreciated, flexibility and low weight are desirable features to have in the fabric since these characteristics facilitate the construction of the airbags once manufacture of the fabric is completed. Such flexibility and low weight are also desirable in the packaging of the final airbag product in the relatively tight confines of standard airbag modules which must be mounted within the steering column or dashboard of a vehicle.
In light of the background above, it can be seen that there is a need for an airbag fabric which provides controlled low air permeability while maintaining flexibility and light weight and which does not require extensive curing or heat treatment processes in its manufacture. The present invention provides such a fabric and therefore represents a useful advancement over the present art.